Field of the Invention
Embodiments of the invention relate to composite centrifugal impellers for turbomachines and related production methods, particularly, but not exclusively, for oil and gas applications.
Other embodiments generally relate to a mold for producing this centrifugal impeller, some particular components to make this centrifugal impeller with this mold, and a turbomachine in which said impeller could be used.
Description of the Related Art
A component of a centrifugal turbomachine is the centrifugal impeller, which transfers, in general, energy from the motor that drives the turbomachine to a working fluid being compressed or pumped by accelerating the fluid outwards from the center of rotation; the kinetic energy imparted by the impeller to the working fluid is transformed into pressure energy when the outward movement of the fluid is confined by a diffuser and the machine casing. This centrifugal machine is called, in general, a compressor (if the working fluid is gas) or a pump (if the working fluid is a liquid).
Another type of centrifugal turbomachine is an expander, which uses the pressure of a working fluid to generate mechanical work on a shaft by using an impeller in which the fluid can be expanded.
U.S. Pat. No. 4,676,722 describes a wheel for a centrifugal compressor made by a plurality of fiber loaded scoops. A disadvantage of this particular impeller is that the various scoops have direct fiber reinforcement substantially in the radial direction, so it is difficult to balance circumferential stress as generated by centrifugal forces at a high speed of rotation. After manufacturing, the sectors are joined to each other by the adhesive strength of a bonding agent, which limits the maximum speed of operation. Also, the method of manufacture, in which the assembly is drawn into place by filaments, is restricted to relatively simple geometries (e.g. with straight-edged sectors) which may have low aerodynamic efficiency.
U.S. Pat. No. 5,944,485 describes a turbine of thermo-structural composite material, particularity one of large diameter, and a method for manufacturing the turbine that provides mechanical coupling for its assembly by means of bolts, grooves, slots, and so on. A disadvantage of this impeller is that the mechanical coupling cannot ensure a high resistance at high rotational velocity when using either a corrosive or erosive working fluid. Therefore the reliability of this component may decrease dramatically. In addition, the scheme for attaching the airfoil to the hub provides user continuous fibers around the internal corners of the passages. Since these are typically areas of high stress, it is desirable to have fibers that are continuous from the airfoil to the cover and from the airfoil to the hub.
U.S. Pat. No. 6,854,960 describes a segmented composite impeller or propeller arrangement and a manufacturing method. The main disadvantage of this impeller is that it relies on adhesive bonding to join identical segments. As a result, it does not have a high mechanical resistance to work at high rotational velocity, and centrifugal forces can separate identical segments and destroy the impeller itself. Another disadvantage is that it is not possible to build an impeller with vanes with complex geometry, as is the case with three dimensional or similar impellers.
In general, a disadvantage of all the aforesaid impellers is that they present a relatively complex mechanical structure, because they are composed of several different components that need to be made independently and then mechanically assembled together. Moreover, the components made of fibers have to be built in general by expensive metal molds, increasing the cost of manufacture. Also, different metal molds have to be used to build these fiber components for each different type of impeller, which significantly increases the cost of manufacture. Again, these mechanical assemblies are not easily achievable by means of automated machinery, further increasing the lime and cost of manufacture.
Another disadvantage is that the vanes of these impellers are not protected in any way from solid or acid particles suspended in the working flow, therefore erosion and corrosion problems could be significant and may lead to the destruction of the component.
Yet another disadvantage is that it may be difficult to achieve the mechanical assembly of all the components needed for optimal operations of the impeller at high speed. Moreover, any distortion produced by the tensions and forces created during use can cause problems during operation, especially at high speed; vibrations may occur during operation, caused by wear and/or by a faulty assembly of various components. Therefore, the impeller may fail.
To date, notwithstanding the developments in technology, these disadvantages pose a problem and create a need to produce simple and inexpensive centrifugal impeller for turbomachinery in an even faster and less expensive way, while at the same time producing an improved and high quality finished product. A particular need exists to produce an innovative centrifugal impeller by taking advantage of composite and fiber technologies, whilemostly preserving the mechanical, fluid-dynamic and aerodynamic properties of metallic impeller, in order to effectively use this innovative impeller in the turbomachinery field. Design improvements are needed to take greater advantage of the inherent strengths of composites, and to enable safe operation at higher tip speeds than is possible with typical metallic impellers.